Re: Splitting in while loop

#!/usr/bin/perl

use strict;
use warnings;

while (split(/[, ]+/, <DATA>))
{
  chomp;
  print "'$_'\n";
}

__DATA__
me@here.com
those@there.com  others@there.com
you@there.com,them@there.com
[download]

Outputs:

Use of uninitialized value $_ in scalar chomp at ./pm11137286.pl line 
+8, <DATA> line 1.
Use of uninitialized value $_ in concatenation (.) or string at ./pm11
+137286.pl line 9, <DATA> line 1.
''
Use of uninitialized value $_ in scalar chomp at ./pm11137286.pl line 
+8, <DATA> line 2.
Use of uninitialized value $_ in concatenation (.) or string at ./pm11
+137286.pl line 9, <DATA> line 2.
''
Use of uninitialized value $_ in scalar chomp at ./pm11137286.pl line 
+8, <DATA> line 3.
Use of uninitialized value $_ in concatenation (.) or string at ./pm11
+137286.pl line 9, <DATA> line 3.
''
Use of uninitialized value in split at ./pm11137286.pl line 9, <DATA> 
+line 3.
[download]

You probably want:

#!/usr/bin/perl

use strict;
use warnings;

for (map { split /[, ]+/ } <DATA>)
{
  chomp;
  print "'$_'\n";
}

__DATA__
me@here.com
those@there.com  others@there.com
you@there.com,them@there.com
[download]

Comment on Re: Splitting in while loop Select or Download Code

Replies are listed 'Best First'.
Re^2: Splitting in while loop by tel2 (Pilgrim) on Oct 07, 2021 at 05:16 UTC
Nice work, thanks for both your solutions, tybalt89! Do you understand why mine wasn't working?	[reply]
Re^3: Splitting in while loop by kcott (Archbishop) on Oct 07, 2021 at 07:43 UTC
G'day tel2, "... why mine wasn't working?" I believe you're working on the erroneous assumption that `split(/[, ]+/, <DATA>)` will assign its result to `$_`. That assignment to `$_` only occurs in a select number of cases. From "perlsyn: Compound Statements": "If the condition expression of a `while` statement is based on any of a group of iterative expression types then it gets some magic treatment. The affected iterative expression types are `readline`, the `<FILEHANDLE>` input operator, ... If the condition expression is one of these expression types, then the value yielded by the iterative operator will be implicitly assigned to `$_`." For each of your `while` iterations, the condition is true three times, once for each DATA line; however, `$_` is not set for any of those iterations. On the fourth iteration, there are no more DATA lines and the loop ends. Always add `use strict; use warnings;` [download] to the top of your code. In this instance, although it wouldn't give a detailed explanation of the problem as I've provided, it would have hinted at a starting point for investigating the issue. — Ken	[reply] [d/l] [select]
Re^4: Splitting in while loop by tel2 (Pilgrim) on Oct 08, 2021 at 00:54 UTC
Thanks for all that, Ken. I tried adding strict & warnings before opening this question, and I got the errors, but I just didn't realise what was going on, but I understand now. Maybe I should have posted it with strict & warnings included, and asked why I'm getting the errors.	[reply]
Re^5: Splitting in while loop by kcott (Archbishop) on Oct 08, 2021 at 04:38 UTC
Re^5: Splitting in while loop by eyepopslikeamosquito (Archbishop) on Oct 08, 2021 at 01:21 UTC
Re^3: Splitting in while loop by AnomalousMonk (Archbishop) on Oct 07, 2021 at 07:44 UTC
Further to jwkrahn's post: tel2: Note that implicit `split` to `@_` has been deprecated for a long time: `Win8 Strawberry 5.8.9.5 (32) Thu 10/07/2021 3:29:50 C:\@Work\Perl\monks >perl -Mstrict -Mwarnings my $data = <<'EOD'; me@here.com those@there.com others@there.com you@there.com,them@there.com EOD open my $fh, '<', \$data or die "opening: $!"; while (split(/[, ]+/, <$fh>)) { chomp @_; print "'$_'\n" for @_; } ^Z Use of implicit split to @_ is deprecated at - line 14. 'me@here.com' 'those@there.com' 'others@there.com' 'you@there.com' 'them@there.com'` [download] Give a man a fish: `<%-{-{-{-<`	[reply] [d/l] [select]
Re^3: Splitting in while loop by AnomalousMonk (Archbishop) on Oct 07, 2021 at 07:21 UTC
`while (split(/[, ]+/, <DATA>)) { ... }` [download] Only a `while`-loop condition expression like `while (<DATA>) { ... }` [download] assigns implicitly to `$_` (see tybalt89's example) (update: but see kcott's post for a more complete discussion of `$_` assignment special-casing). An arbitrary expression like `split(...)` does not. Had you had warnings enabled, Perl would have at least hinted at this problem. Give a man a fish: `<%-{-{-{-<`	[reply] [d/l] [select]
Re^3: Splitting in while loop by jwkrahn (Abbot) on Oct 07, 2021 at 07:21 UTC
`while (split(/[, ]+/, <DATA>))` [download] Is interpreted by perl as: `while ( @_ = split( /[, ]+/, <DATA> ) )` [download]	[reply] [d/l] [select]
Re^4: Splitting in while loop by tel2 (Pilgrim) on Oct 08, 2021 at 00:34 UTC
Thanks jwkrahn, but if they're interpreted to be the same, then why does this code: `while (split(/[, ]+/, <DATA>)) { print @_ }` [download] print nothing, while this code: `#while (split(/[, ]+/, <DATA>)) # Edit: Sorry - ignore this while (@_ = split(/[, ]+/, <DATA>)) # Edit: I meant this { print @_ }` [download] prints: `me@here.com those@there.comothers@there.com you@there.comthem@there.com` [download] ? Update: Cancel the above. I see AnomalousMonk's answer to it now.	[reply] [d/l] [select]
Re^5: Splitting in while loop by kcott (Archbishop) on Oct 08, 2021 at 03:23 UTC
Splitting Hairs [tangent to: Splitting in while loop] by pryrt (Abbot) on Oct 08, 2021 at 13:48 UTC
Some notes below your chosen depth have not been shown here
Re^6: Splitting in while loop by tel2 (Pilgrim) on Oct 08, 2021 at 04:02 UTC
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